Abstract
Soil seed bank composition is important to the recovery of natural and semi-natural areas from disturbance and serves as a safeguard against environmental catastrophe. White-tailed deer (Odocoileus virginianus) populations have increased dramatically in eastern North America over the past century and can have strong impacts on aboveground vegetation, but their impacts on seed bank dynamics are less known. To document the long-term effects of deer browsing on plant successional dynamics, we studied the impacts of deer on both aboveground vegetation and seed bank composition in plant communities following agricultural abandonment. In 2005, we established six 15×15 m fenced enclosures and paired open plots in recently fallowed agricultural fields near Ithaca, NY, USA. In late October of each of six years (2005–2010), we collected soil from each plot and conducted seed germination cycles in a greenhouse to document seed bank composition. These data were compared to measurements of aboveground plant cover (2005–2008) and tree density (2005–2012). The impacts of deer browsing on aboveground vegetation were severe and immediate, resulting in significantly more bare soil, reduced plant biomass, reduced recruitment of woody species, and relatively fewer native species. These impacts persisted throughout the experiment. The impacts of browsing were even stronger on seed bank dynamics. Browsing resulted in significantly decreased overall species richness (but higher diversity), reduced seed bank abundance, relatively more short-lived species (annuals and biennials), and fewer native species. Both seed bank richness and the relative abundance of annuals/biennials were mirrored in the aboveground vegetation. Thus, deer browsing has long-term and potentially reinforcing impacts on secondary succession, slowing succession by selectively consuming native perennials and woody species and favoring the persistence of short-lived, introduced species that continually recruit from an altered seed bank.
Highlights
Large herbivores are often considered keystone species because they can both directly and indirectly alter plant community structure and composition [1,2,3]
While the effects of selective deer browsing on plant community composition and diversity and in delaying forest succession in North America have been well documented (e.g. [3,4,35,36,37]), less is known about how deer browsing may affect these parameters at earlier secondary successional stages such as in recently established old-field communities (e.g. [38,39])
Our findings to date indicate that deer browsing plays a major role in determining the diversity, abundance, and successional progression of plant species in both the seed bank and the aboveground vegetation, likely putting deer accessible and non-accessible areas on divergent trajectories
Summary
Large herbivores are often considered keystone species because they can both directly and indirectly alter plant community structure and composition [1,2,3]. High densities of white-tailed deer (Odocoileus virginianus Boddaert) populations across North America, for example, are having strong impacts on plant communities, shifting vegetation composition and structure [4,5]. Because deer are generalist browsers that thrive in postagricultural habitats, they can directly impact the abundance and dispersal of seeds, and potentially alter seed bank composition during secondary succession. Deer browsing may impact the abundance and diversity of native versus non-native plant species, as disturbance and browsing may shape community dynamics in secondary succession. Relatively few studies in these systems have directly linked the composition of dormant underground propagules with aboveground vegetational dynamics
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